The present invention relates to a method for glazing the printing area in printing with thick deposit of ink onto the plane sheets absorbing said ink slightly or scarcely, and also relates to an apparatus inherently used in the performance of said method wherein the printing operation is carried out by means of an intaglio or lithography printing plate.
The name plates, and more particularly those used in the electric tools or devices for domestic use, tend recently to be required to have various functions other than their traditional function indicating the designation and/or manufacturer. The recently required functions are the effects as a decorative plate attached to said electric goods or as an instructive plate showing the operational manner for said goods. The known printing method such as the photo-etching and the silk screen printing cannot produce such multifunctional name plates. Therefore, a new printing method for the name plates has been developed to meet the requisite mentioned above. There is similar circumstances also in printing with a thick deposit of the resist-ink on the plastic base sheets laminated with copper foils by means of the pattern of a printed circuit. The typical technique for printing the metal or plastic sheets, which cannot absorb the ink, utilizes an intaglio plate without any dampening water and with thick deposit of ink. Said intaglio plate comprises a printing area and a non-printing area, the former being formed by partially eliminating the oil-repellent thin flim on the raw plate so as to make the part lipophilic whereby the rest part of said plate surface remains lipophobic as the non-printing area. For example, the raw plate consists of an elastic base layer covered with an oil-repellent layer comprising a silicone rubber having in its molecule some photosensitive groups, said elastic layer being made of natural or synthetic rubber. The abovementioned raw plate is exposed through a predetermined pattern and then developed so as to selectively eliminate the parts of said oil-repellent layer thereby to form ink staying recesses serving as a whole as an image area. The remaining oil-repellent portions serve also as a whole as a non-printing area of the printing plate. The thus prepared printing plate is then fixed onto the plate cylinder for the aforedescribed intaglio printing of the objects such as metallic sheet and plastic sheet incapable of absorbing the ink so as to directly print them with thick deposit of the ink but without any dampening water.
In the intaglio printing without use of the dampening water, such an ink is utilized that the transferability from the printing plate to the objects to be printed improved by increasing its viscosity up to, for instance, 1000 poise. The printing speed may also be made slower, for instance, down to 200-300 mm/sec so that a higher transfer energy may be imparted to the ink. As shown diagrammatically in FIG. 1, the ink 1 will be transferred from the printing area of the printing plate to the non-absorbent object 2 such as a metallic sheet wherein the ink solution splits into some clods partially interconnected with each other. FIG. 2 illustrates also a diagrammatic change in the shape of said highly viscous ink after it has been transferred to the object 2 to form a desired image 3 thereon. The change occurs, as the time passes, in such a manner that the surface of the ink forming the image 3 becomes flatter and flatter by virtue of the surface tension of said ink. It is to be noted, however, that in despite of the apparent or superficial macroscopic uniformity in the thickness of said ink forming the image 3 (the thickness being approximately equivalent to 50-30% of the ink thickness previously transferred from inking rollers to said printing plate), the surface of said ink assumes an uneveness like as rippling waves when seen microscopically whereby the light is reflected diffusely to make said surface dim or blurred. This is an unwelcome defect in the kind of the name plate which must have a beautiful surface as one of its important functions or merits. Further, there is still another problem that said ink includes many small bubbles therein, not shown in FIG. 2, which are sealed as pinholes in said ink having a great thickness 7 to 8 .mu.m when it becomes dry and hardened. An apparent density of said ink layer also will be consequently decreased undesirably to result in a poorer resistance against the etching solution used in the production of base plate for the printed circuits.
According to a known proposal for solving the problems, a larger amount of solvent is admixed with the ink so as to reduce the ink solution viscosity for the purpose of accelerating the natural levelling off effect of the thick deposited ink on the printing area. This is, as will be appreciated, inconsistent with the necessity for improving the ink transferability by means of the higher viscosity of ink in the printing with thick deposit of it. Namely, in such a proposed method, the ink solution will act on the object so soft that an accurate ink transfer thereto from the printing area of printing plate becomes comparatively difficult thereby a fine printing becoming almost impossible.